Heaters



March 7, 1967 T. N. STACK 3,307,530

. 7 HEATERS Original Filed April 6, 1964 N f) s m INVENTOR. 571mm: A! 5 714m TOP/V575" United States Patent 3,307,530 HEATERS Thomas Noel Stack, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Original application Apr. 6, 1964, Ser. No. 357,591. Dr-

vided and this application Sept. 14, 1966, Ser. No. 579,235

3 Claims. (Cl. 126116) This application is divided from my copending application Serial Number 357,591, filed April 6, 1964.

This invention relates to space heaters and particularly to space heaters of relatively compact size employing wedge-shaped ceramic heat-exchangers.

It is one object of this invention to provide space heaters of compact size. An additional object of the invention is to provide heat-exchanger assemblies having enhanced efliciency. Another object of this invention is to provide burners for combustible mixtures of improved design. Other objects will become apparent from the reading of my present disclosure.

It has been found that ceramic heat-exchangers of the cross-flow type are conveniently employed when mounted in a metallic frame which permits of coupling to other equipment. I have found that especially useful results are achieved by employing a wedge-shaped cross-flow heat-exchanger forced into frictional engagement with a metallic frame and restrained from gradual disengagement.

It will be understood that a cross-flow heat-exchanger is one in which heat is exchanged between two fluids travelling generally at about right angles to one another.

For a wedge-shaped heat-exchanger, one stream of gases passes through normal to one face (which may be designated the bottom for convenience) and emerges from the opposite parallel face (conveniently designated the top). The second stream, however, passes through an inclined face in a direction at approximately right angles to the first stream and emerges from the opposite nonparallel face which may also be inclined.

Inclination of these non-parallel faces in the heat-exchangers useful for this invention is at an angle of about 5 to 12 from perpendicular to the bottom, that is the inclined face makes an angle of about 78 to 85 to the bottom face. Preferably the total inclination of the two faces together is not more than about 15, that is if extended they would meet at an angle of from 5 to about 15 At greater angles frictional engagement is less satisfactory and at lesser angles it is more difficult to achieve frictional engagement.

Further consideration of space heaters of the invention will be more clearily understood by reference to the accompanying drawings wherein:

FIGURE 1 is a side elevation to reduced scale of a space heater of the invention partially broken away to a vertical section.

FIGURE 2 is a cross-section of a space heater of the invention along line 22 of FIGURE 1 and is also to a reduced scale.

Referring now to the details of the figures, wherein identical parts bear the same indicia, it will be seen that the space heater of FIGURES 1 and 2 consists of three parts, a flue gas manifold 10, a heat-exchanger assembly 20 and a burner assembly 50. The flue gas manifold may be of any convenient type for adaptation of the heatexchanger assembly to suitable venting equipment (not shown) which desirably incorporates means such as a suction fan for overcoming back pressure from the heatexchanger. Slight suction used in educting combustion products by whatever means effected further safeguards against leakage of such products into the air-stream because of porosity or cracks developing in the flat sheets 36.

The heat-exchanger assembly 20 comprises an outer casing 22 having an opening at the top to the flue gas assembly, at the bottom to the burner and on the front and back faces. The ends are closed. The opening on the front face is seen in FIGURE 1 to be smaller in area than the surface of ceramic heat-exchanger 30 so that-rim means, a relatively narrow engagement face 24, is provided around the edge of opening 26 as is also to be noted in the cross-sectional view of FIGURE 2. At least one of the open faces of casing 22 tapers inward toward the top at an angle of about 5 to 12 (both are shown thus tapered in FIGURE 2).

Heat-exchanger 30 is broken away in FIGURE 2 to show alternation of axes of corrugation (32 vertically corrugated, 34 horizontal corrugated) and separation of successive corrugated sheets, i.e. 32 and 34, by flat sheets 36. In FIGURE 1 it will be seen that peripheral vertical passageways are cut by the inclined face. The upper and lower edges of heat-exchanger 30 are shown with at least these passages plugged by filling 38. Other means effecting blockage of peripheral channels may be employed, thus it will be seen that these passages are blocked at the top by the widened flange of flue gas manifold 10 and gasket 12 and at the bottom by burner liner 52 and gasket 51. Cross hatching lines on thin sheets shown in section are not shown in the drawings to avoid confusion.

Heat-exchanger 30 is constructed of refractory materials, very suitably zircon-mullite, petalite-silica or the like, and is pressed into casing 22 with sufiicient force that it frictionally engages with engagement face 24 around both faces. faces of casing 22 must be finished to a suflicient degree to avoid irregularities such as welds, blisters, bumps, etc. which might prevent proper engagement or might gouge the faces of heat-exchanger 30. Heat-exchanger 30 is constructed to be slightly oversize and the faces are then finished to the proper taper by sanding, or other procedure as will be evident to those skilled in the art, and the heatexchanger is forced into casing 22 avoiding so much force as would crush the ceramic of the heat-exchanger. The upper and lower faces are then finished flush with the flanges 28 of casing 22. Frictional engagement is sufficient to retain heat-exchanger 30 within the casing and to maintain substantially gas-tight dihedral sealing at the angles between the faces and the top and bottom respectively throughout any operating cycle. A small amount of grouting may be employed around the edges if desired but is not necessary when the heat-exchanger assembly is carefully constructed in accordance with my teachings.

Heat-exchanger assemblies of the invention may be constructed in which the length is up to about twice the height, say about one foot long, either by employing two heat-exchangers of the type shown in FIGURES 1 and 2 or one larger heat-exchanger constructed in accordance with my teachings. Greater lengths than that, i.e having greater heat-exchange capacity are desirably achieved by using several smaller assemblies inasmuch as the longitudinal engagement faces (e.g. those at top and bottom) become so long as to be subject to some warpage in use and gas-tight sealing is no longer possible. This results in exacerbation of deterioration and warpage.

Heat-exchanger assemblies of the invention, which may be referred to conveniently as wedge-shaped or keystone heat-exchanger assemblies, are particularly useful with burners of the type disclosed which serve as means urging the heat-exchanger into engagement with the frame. Referring again to the FIGURES 1 and 2 where a suitable burner assembly 50 is shown, it will be seen that the liner 52 of the burner is relatively thick ceramic material overlapping the edges of heat-exchanger and in cooperation It will be evident that the inner sura with ceramic gasket or packing 51 urges or retains heat-exchanger 30 in frame 22. Burner assembly 50 will be seen to have a metal casing 53 with flange 48 and refractory ceramic liner 52, ignition means 54, port 56 for admission of combustible mixture into combustible mixture plenum 58 and burner grid 60 conveniently constructed of refractory ceramic with a multiplicity of vertical passageways and cemented in place. It will be evident that the liner 52 may be rabbetted to provide a seat for burner grid 60 if desired.

Space-heaters of the invention, as shown in FIGURES 1 and 2, and including such heaters employing alternative burner assemblies, possess certain unusual and remarkable features. Although one might expect such a device to operate very hot, and in fact in operation the interior of the heat-exchanger may indeed by very hot (of the order of 1500) the dead spaces around the periphery of the heat-exchanger prevent excessive rise in temperature of the casing. This effect, which may be characterized as peripheral insulation, assists in maintaining compressive forces on the heat-exchanger under all operating conditions inasmuch as expansion of the casing does not exceed that of the heat-exchanger itself. The dihedral seals are thus retained intact so long as warpage of the frame is avoided. The efficiency of space heaters of the invention is such that large volumes of air are heated readily by small heaters.

What is claimed is: 1. A hot air space heater comprising in combination (I) a combustion chamber, (II) means providing a combustible mixture to said combustion chamber, (III) ignition means within said combustion chamber and, connected to said combustion chamber, (IV) at least one cross-flow ceramic heat-exchanger unit-consisting essentially of (A) a metallic frame, having four open faces and closed ends, (B) not more than two cross-flow ceramic heatexchan-gers having (1) two parallel faces and a multiplicity of passageways therebetween open to receive and educt combustion products from said combustion chamber and further having (2) at least one and not more than two inclined faces frictionally engaging said frame at the edges and adapted to receive cool air and deliver heated air,

(C) means urging said heat-exchangers into continuous frictional engagement with said frame,

(D) means for educting combustion products from said combustion chamber through said heatexchanger.

2. A heat-exchanger assembly consisting essentially in combination (A) a metallic frame having four open faces and closed ends, two of said faces being parallel and unequal in area and at least one other face being inclined to said parallel faces, said parallel faces having attachment means and the others of said open faces having inward rim means,

(B) not more than two cross-flow heat-exchangers within said metallic frame and frictionially engaging said frame at least along the inward rim means of one of the non-parallel faces thereof consisting essentially of courses of passageways having axes in successive courses substantially at right angles connecting between opposing open faces of said frame and having means closing off at least those of said passageways connecting between adjacent open faces of said frame.

3. A heat-exchanger assembly consisting essentially in combination (A) a metallic frame having four open faces and closed ends, two of said faces being parallel and unequal in area and at least one other face being inclined to said parallel faces, said parallel faces having attachment means and the others of said open faces having inward rim means,

(B) not more than two cross-flow heat-exchangers within said metallic frame and frictionally engaging said frame at least along the inward rim means of one of the non-parallel faces thereof consisting essentially of courses of passageways having axes in successive courses substantially at right angles connecting between opposing open faces of said frame and having at least a part of said peripheral passageways adjacent to the non-parallel faces closed to passage of hot gases whereby said frame is insulated from direct contact with heat fluid passages.

References Cited by the Examiner UNITED STATES PATENTS JAMES W. WESTHAVER, Primary Examiner. 

1. A HOT AIR SPACE HEATER COMPRISING IN COMBINATION (I) A COMBUSTION CHAMBER, (II) MEANS PROVIDING A COMBUSTIBLE MIXTURE TO SAID COMBUSTION CHAMBER, (III) IGNITION MEANS WITHIN SAID COMBUSTION CHAMBER AND, CONNECTED TO SAID COMBUSTION CHAMBER, (IV) AT LEAST ONE CROSS-FLOW CERAMIC HEAT-EXCHANGER UNIT CONSISTING ESSENTIALLY OF (A) A METALLIC FRAME, HAVING FOUR OPEN FACES AND CLOSED ENDS, (B) NOT MORE THAN TWO CROSS-FLOW CERAMIC HEATEXCHANGERS HAVING (1) TWO PARALLEL FACES AND A MULTIPLICITY OF PASSAGEWAYS THEREBETWEEN OPEN TO RECEIVE AND EDUCT COMBUSTION PRODUCTS FROM SAID COMBUSTION CHAMBER AND FURTHER HAVING 